As is well known to those skilled in the art, lubricating oils which are used in internal combustion engines are degraded to acidic products which attack and corrode engine parts and catalyze the formation of sludge. As a result, the lubricity of the oil is reduced; and wear on the engine parts is accelerated.
In order to neutralize the effect of the acids so formed, it is desirable to add basic substances to the lubricating oil; and these neutralize the acids before they attain a high enough concentration to cause significant damage. Typical of the compositions which maybe added are colloidal carbonates of alkaline earth metals; and they are usually added as carbonate dispersions stabilized by oil-soluble surface active agents. These latter are commonly oil-soluble alkaline earth metal salts of sulfonated petroleum lubricating oil fractions--made by sulfonating lubricating oil fractions (of molecular weight of typically 350-600) or by sulfonating alkyl benzenes of desired molecular weight. Alkylated benzenes prepared from straight chain alkyl groups are preferred.
Preparation of overbased calcium sulfonates typically is effected by reacting an alkylbenzene sulfonic acid (dissolved in oil) with calcium oxide or calcium hydroxide and bubbling carbon dioxide through the reaction mixture. The final overbased product contains an excess of calcium carbonate together with a calcium sulfonate.
Overbased compositions may be characterized inter alia by Total Base Number (TBN) as determined by ASTM Test D-2896. This is the number of equivalent milligrams of KOH needed to neutralize one gram of sample to a pH of 7. Commonly the TBN may be 0-500.
U.S. Pat. No. 4,954,272 discloses the preparation of an overbased oil-soluble calcium sulfonate (having a TBN of 325) by (i) mixing a neutral calcium sulfonate with a hydrocarbon and a lower alkanol; (ii) adding CaO, Ca(OH).sub.2 and H.sub.2 O in mole ratio of CaO to Ca(OH.sub.2) of about 9-0.25:1 and of H.sub.2 O to CaO of about 0.15-0.30-1; (iii) heating to about 100.degree. F.-170.degree. F./0-50 psig; (iv) admitting carbon dioxide for 60-140 minutes; (v) adding diluent oil; (vi) separating solids from the solution of overbased sulfonate in oil and hydrocarbon; and (vii) stripping hydrocarbon.
U.S. Pat. No. 4,427,559 discloses that a mixture of calcium oxide and calcium hydroxide can be used in the overbased reaction to provide reserve alkalinity to neutral calcium sulfonates. It is reported that when mixtures containing up to 30 percent CaO are used, satisfactory 400 TBN overbased sulfonate products are obtained. When mixtures of 30 to 50 percent CaO are used, a gelatinous material which plugs the filter is obtained. Concentrations of CaO above 70 percent produce a fluid product containing finely divided particles which can not be filtered and which are reflective of light. In this regard, the patent teaches the criticality of the ratio of the calcium oxide the calcium hydroxide in the absence of a promoter in producing acceptable product.
Other references which may provide additional background may include
U.S. Pat. No. 4,810,396 PA1 U.S. Pat. No. 4,604,219 PA1 U.S. Pat. No. 4,165,291 PA1 U.S. Pat. No. 4,137,184 PA1 U.S. Pat. No. 4,824,584 PA1 U.S. Pat. No. 4,086,170 PA1 (i) forming a reaction mixture containing a neutral alkaline earth metal salt of an alkaryl sulfonate, an alkaline earth metal halide, a hydrocarbon diluent-solvent, a lower alkanol promoter, and an alkaline earth metal oxide; PA1 (ii) heating said reaction mixture to 50.degree. C.-70.degree. C.; PA1 (iii) adding water to said heated reaction mixture; PA1 (iv) after termination of water addition, admitting gaseous carbon dioxide to said reaction mixture in molar amount less than the molar amount of alkaline earth metal oxide originally added to said mixture thereby forming an overbased composition containing an oil-soluble alkaline earth metal salt of an alkaryl sulfonate; and PA1 (v) recovering said overbased composition containing an oil-soluble alkaline earth metal salt of an alkaryl sulfonate; PA1 (i) The Witco Cal T brand of a mixture containing 65% of sulfonated alkylated petroleum hydrocarbon (as its neutral calcium salt) and 35% of "synthetic" sulfonated alkylated benzene (as its neutral calcium salt). This petroleum based component is prepared from a petroleum fraction of 300-700 molecular weight which bears a long chain alkyl group (one per molecule) which is sulfonated to yield product containing predominantly one --SO.sub.3 H per molecule, followed by neutralizing with calcium hydroxide. PA1 (ii) The Witco Cal T-2 brand of a mixture containing the same components as does the Witco Cal-T product --but in equal portions by weight. This product contains no significant amount of calcium chloride. PA1 (i) a desirable low Overbasing OB Ratio of 7-10:1, preferably abut 8.5:1 as measured by the molar ratio [CaCO.sub.3] .div.[SO.sub.3 H.sup.-1 ] in the final product. This provides a proper balance between the "soap content" and the "alkalinity" (typical prior art products having the same calcium and sulfonate content, are undesirably characterized by a much higher OB Ratio). PA1 (ii) a content of undesirable crystalline calcium carbonate of typically less than 0.5w %; PA1 (iii) a kinematic viscosity at 100.degree. C. of less than about 100 CSt; PA1 (iv) a sulfonate content greater than about 29%, typically 30%-34%, say 32.9%; PA1 (v) a calcium content greater than about 9%, typcally 10%-14%, say 12.1%. PA1 (i) The volume of solid by-products (which must be disposed of) is typically reduced by about a third and commonly by half. Prior art processes commonly yield a solid volume of about 9-10% of the reaction mixture while the process of this invention commonly yields 6% or less. PA1 (ii) the addition of water, preferably in one aliquot, prior to admission of carbon dioxide, eliminates the need to control water addition during carbon dioxide admission as is true of prior art techniques. PA1 (iii) the elimination of the need to add calcium hydroxide (with the charge calcium oxide) decreases the number of solid charge materials to be controlled. PA1 (iv) the mole ratio of charge calcium oxide to charge calcium alkaryl sulfonate (maintained at less than 10:1) permits attainment of a clear product containing a decreased content of solids. PA1 (v) the undesirable formation of crystalline calcium carbonate (which has low solubility in oils)--which would normally be expected at high CaO content--is prevented. PA1 (vi) engine performance is improved.
It is an object of this invention to provide an improved method of preparing overbased calcium sulfonates. Other objects will be apparent to those skilled in the art.